Jackup drilling unit having material storage in jacking legs

ABSTRACT

A jackup mobile offshore drilling unit includes a hull and a plurality of jacking legs movable longitudinally with respect to the hull and having features thereon to support the hull above a body of water. A storage tank is disposed inside at least one of the plurality of jacking legs. The unit comprises means for moving the storage tank longitudinally inside the at least one of the plurality of jacking legs.

BACKGROUND

This disclosure is related to the field of mobile offshore drilling units (MODUs). More specifically, the disclosure relates to jackup type MODUs which may be self-propelled and have storage capacity within the jacking legs to increase the available deck load of the drilling unit.

Jackup type MODUs (“jackups”) known in the art include a water-tight hull capable of flotation in a body of water. The hull may include wellbore drilling apparatus supported by the hull, fluid and supply storage in the hull, living quarters for personnel and power generation equipment. Jackups known in the art include three or more jacking legs movably coupled to the hull, typically through openings therefor through the hull proximate the perimeter of the hull. The jacking legs are most commonly truss-type structures, although cylindrical and other type structures are known for such purpose. The jacking legs may be longitudinally movably connected to the hull through various forms of a rack or similar gear-tooth structure, wherein the rack engages a jacking motor coupled to the hull. Rotation of the jacking motor causes the associated jacking leg to move downwardly to the water bottom and then to lift the hull out of the water to a selected distance above the mean water level (the “air gap”). Opposite rotation of the jacking motor causes the associated jacking leg to be lifted, such that the hull is lowered into the water (and thus be buoyantly supported) and the legs lifted from the water bottom to enable the hull to move along the water surface.

Jackups known in the art are typically barges, that is, they can move on the water surface only by being towed by one or more tow vessels. Jackups known in the art typically have the wellbore drilling apparatus disposed to one side of the hull. Earlier design jackups provided such arrangement by having the drilling apparatus positioned over a recessed feature formed in the perimeter of the hull. More recent design jackups have the drilling apparatus movable mounted to cantilever beams, whereby the drilling apparatus may be positioned substantially fully within the perimeter of the hull during movement of the jackup, and moved or “skidded” to a position outside the perimeter of the hull when the drilling apparatus is used to drill a wellbore below the water bottom.

A consideration in design and use of any particular jackup for any particular wellbore to be drilled is the “variable deck load” capacity of the hull. The variable deck load may include the weight of components and items that may be specific to a particular wellbore, for example, an amount of drilling fluid to be stored in tanks disposed in the hull, the total amount of drill pipe, drilling riser, drilling tools and well casing that must be carried on or in the hull in order to construct the wellbore and amounts of fuel, lubricants and other fluids, e.g., potable water, that must be carried by the hull to support drilling operations. To the extent that such components and other items may be supported other than by the hull, it may be possible to increase the effective drilling capacity of a particular jackup by enabling more drill pipe, drilling tools, drilling riser and casing to be supported by the hull.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a side elevation view of an example jackup drilling unit according to the present disclosure.

FIG. 2 shows an example embodiment of a jacking leg according to the present disclosure.

FIG. 3 shows an example embodiment of a leg jacking system having an internal storage tank.

FIG. 4 shows an automatic control system for maintaining a selected elevation of a storage tank inside a jacking leg.

DETAILED DESCRIPTION

An example mobile offshore drilling unit is shown in FIG. 1 at 10. The drilling unit 10 in the present example is called a “jackup” drilling unit, as explained in the Background section herein. Such drilling units are supported at the water bottom 20 by jacking legs 12 that can be moved along their longitudinal direction with respect to a hull 14C of the drilling unit 10 by operating jacking motors 12B. the jacking legs 12 in the embodiment shown in FIG. 1 may be cylindrically shaped.

The jacking motors 12B may each turn a respective gear unit (not shown) the output of which is in contact with a rack 12A or similar linear gear-toothed structure disposed on the jacking leg 12 and extending along a substantial portion of its length. Other types of jackup drilling rigs may use a pinhole/hydraulic jacking system to move the legs, for example. An example of such jacking system will be further explained with reference to FIG. 3. The jacking legs 12 may include a “spud can” 12C at a bottom end thereof for contacting the water bottom 20 and supporting the weight of the drilling unit 10. During set up of the drilling unit 10 on a well location, the hull 14C floats and may be moved to the selected location by tug boats or similar towing vessels as the legs 12 are maintained substantially in their uppermost position with respect to the hull 14C. The jacking legs 12 are positioned within and move within corresponding openings 14D in the hull 14C. Such openings 14D provide a path through the hull 14C for the jacking legs 12, but are sealed on their interior surface so that water is excluded from entering the interior of the hull 14C.

When the unit 10 is positioned at the selected location, the hull 14 is positioned both geodetically and with the hull 14C in a preferred geodetic orientation. The jacking legs 12 are moved longitudinally (called “jacking”) using the jacking motors 12B (or hydraulic motors in hydraulically jacked leg examples as shown in FIG. 3). Downward movement of the jacking legs 12 with respect to the hull 14C eventually causes the spud cans 12C to contact the water bottom 20. When the spud cans 12C contact the water bottom 20, continued movement of the jacking legs 12 with respect to the hull 14C causes the hull 14C to move upwardly out of the water. The jacking continues until the hull 14C is positioned at a selected height (“air gap”) 22 above the mean water surface 18.

When the selected air gap 22 is obtained, a cantilever structure (“cantilever”) 14 may be laterally displaced from its transport position generally over the hull 14C. Such lateral displacement, called “skidding out” the cantilever 14, may be performed by a cantilever skid motor 14B that rotates a gear (not shown) in contact with a cantilever skid rack 14A. Other examples of a cantilever may use a pinhole/hydraulic skidding unit in contact with the cantilever skid rack 14A. The skid out continues until a drilling rig 29, supported generally near the outward end of the cantilever 14, is positioned over a proposed well location 31 on the water bottom 20. The drilling rig 29 may include pipe lifting, supporting and rotating devices familiar to those skilled in the art, for example, a derrick 24 in which is included a tubular or pipe rack 32 to vertically support assembled “stands” of tubulars 34 used in wellbore drilling, testing and completion operations. The drilling rig 29 may include a winch called a drawworks 26 that spools and unspools wire rope or cable, called “drill line” 27, for raising and lowering a traveling block and hook 28. The hook 28 may support a top drive 30 or similar device for applying rotational energy to the pipe for various drilling and well completion operations.

In the present example, sensors may be associated with some of the foregoing drilling unit components to measure one or more parameters used in some types of data recording systems. The parameters measured by the various sensors described herein may be characterized as being related to the beginning and the end of one or more “auxiliary operations.” As used in the present description, the term “auxiliary operations” is intended to mean any function or operation on the drilling unit 10 that is not related to equipment or devices being inserted into or removed from a wellbore (including the active drilling of such wellbore), but is nonetheless essential to enabling the drilling unit 10 to perform intended drilling operations. The above examples of jacking the legs 12 until the selected air gap 22 is obtained, as well as skidding the cantilever 14 are two of such auxiliary operations.

As an example, each jacking motor 12B may include a sensor and an associated wireless data transceiver (shown at 11 collectively) for measuring electric current drawn by the respective jacking motor 12B. A similar wireless transceiver/sensor combination 11 may be associated with the cantilever skid motor 14B. A transponder, such as an acoustic or laser range finder, or a global positioning system receiver, shown at 36, may be disposed proximate a bottom surface of the hull 14C in order to measure the air gap 22. Such sensor 36 may also include an associated wireless transceiver 11. A data acquisition system (“DAQ”) 33 may be disposed at a convenient position on the drilling unit 10 and include a wireless transceiver 11A for receiving data from the various sensors, such as those described above. Although in the present example the various sensors include wireless transceivers 11 to communicate with the DAQ 33, it should be clearly understood that “wired” sensors may also be used in accordance with the invention.

The drilling rig 29 may also include sensors for measuring various parameters related to operation of the drilling rig 29. An example of such sensors and methods for validating and interpreting the measurements made by the rig sensors to automatically determine what drilling operation is underway at any time are described in U.S. Pat. No. 6,892,812 issued to Niedermayr et al. and incorporated herein by reference. As shown in FIG. 1, one such sensor is can be a load cell 27A arranged to determine the total axial force (weight) supported by the drilling unit 29. The load cell 27A may be coupled wirelessly through a transceiver 11 to the DAQ 33. Such load cell is generally known in the art as a “weight indicator.” Another sensor may be a pressure/volume sensor 126 associated with pumps (not shown) configured to move fluid through appropriate rotary seals in the top drive 30 and into any pipe coupled to the top drive, such as a drill string or casing. The pressure/volume sensor 126 may include a pressure transducer (not shown separately) and a device known in the art as a “stroke counter” or similar device that measures a parameter related to the volume displacement of pistons within cylinders in a “mud pump.” The pressure volume sensor 126 may also be wirelessly coupled to the DAQ 33. The weight indicator (load cell 27A) and the pressure/volume sensor 126 may be used to make measurements related to the start and stop times of various operations. The foregoing sensors may be used in some examples to identify and record start and stop times of auxiliary operations as more fully set forth in U.S. Pat. No. 7,886,845 issued to King et al. It should be understood that the foregoing sensors and DAQ 33 in the present example are not intended to limit the scope of the present invention but are described only to illustrate one example embodiment of a jackup drilling unit. In the present example embodiment, an elevation sensor 124 may be affixed proximate the top of one or more of the jacking legs 12 to communicate a signal to the DAQ 33 indicative of the jacking position with respect to the hull 14C of the associated jacking leg 12. Use of the measurements from such sensor 124 will be further explained with reference to FIGS. 2 and 4. The elevation sensor 124 may be an acoustic sensor, a capacitance proximity sensor, magnetic proximity sensor or any other sensor that enables determination of the longitudinal position of the jacking leg 12 with respect to the hull 14C.

FIG. 2 shows an example of one of the jacking legs 12 according to the present disclosure in more detail. The jacking leg 12 may be formed substantially as a hollow cylinder. The previously described spud can 12A may be disposed at the bottom of the jacking leg 12. A storage tank 25 may be disposed in the interior of the jacking leg 12. The interior of the jacking leg 12 and the exterior surface of the storage tank 25 may be suitably shaped to enable the storage tank 25 to move longitudinally within the interior of the jacking leg 12. One or more cable sheaves 17B may be affixed to a top end of the storage tank 25. A like number of cable sheaves 17B may be affixed proximate an upper end of the jacking leg 12. A cable 17, for example, made from wire rope or the like, may extend from a winch 21 affixed in a suitable location on the hull 14, through a first sheave 17A, through the one or more sheaves 17B both at the upper end of the jacking leg 12 and on the top of the storage tank 25, to a fixed end which may be on the storage tank 25, the hull 14C or the jacking leg 12. The winch 21 may include a sensor 21A such as a rotary encoder or other sensor for measuring rotation of the winch, and consequently, an amount of the cable 17 that is extended from the winch at any time. Signals from the sensor 21A may be used to determine the elevation of the storage tank 25 inside the jacking leg.

One or more fluid transfer hoses 19 may be stored on a constant tension reel 23, and may extend to the top end of the jacking leg over a hose sheave 19A configured for the number of fluid transfer hoses used in any particular embodiment. The one or more fluid transfer hoses 19 are in fluid communication with the interior of the storage tank 25. Fluid may be moved into and out of the storage tank 25 by any known method, for example, air or inert gas pressure displacement, or buoyant liquid displacement.

In the present example embodiment, operation of the winch 21 may be synchronized with longitudinal movement of the jacking leg 12 so that the storage tank 25 is maintained at a same elevation with respect to the hull 14C as the jacking leg 12 is moved from its fully raised position as shown in the figures to its fully lowered position. In the present example embodiment, the storage tank 25 may be maintained at an elevation such that it is entirely disposed between the uppermost deck surface of the hull 14C, i.e., entirely within the jacking leg opening (14D in FIG. 1), and entirely above the water surface 18. As will be appreciated by those skilled in the art, by maintaining the elevation of the storage tank 25 above the water surface 18 at all times, the storage tank may store water-immiscible and/or hazardous fluids such as engine fuel without the need to provide the storage tank 25 with a double walled construction. Further, because the weight of the storage tank 25 is transferred to the jacking leg 12 through the cable 17, the hull 14C does not support any part of the weight of the storage tank 25. Thus, the weight of the storage tank 25 may be made available as part of the available variable deck load of the jackup drilling unit (10 in FIG. 1). Further, because the storage tank 25 may be maintained at an elevation inside the jacking leg 12 substantially always within the jacking leg opening (14D in FIG. 1) in the hull 14C, the portion of the jacking leg 16 in which the storage tank 25 is suspended may be further protected from damage by collision with objects in the water.

In other embodiments, the storage tank 25 may be moved to any other selected elevation with respect to the hull 14C or maintained at any other selected elevation with respect to the water surface 18.

In some embodiments, a storage tank and winch structure as shown in FIG. 4 may be included in any or all of the jacking legs in a jackup mobile offshore drilling unit according to the present disclosure.

FIG. 3 shows an example jacking apparatus 12D that may be disposed a jacking house in each jacking leg opening (14D in FIG. 1). The jacking apparatus may be of a type commercially available from GustoMSC B. V., Karel Doormanweg 25, 3115 J D Schiedam, The Netherlands. Such jacking apparatus may be configured for continuous jacking leg movement during jacking operations. The jacking apparatus 12D may include a frame 118 onto which are mounted a plurality of double acting hydraulic cylinders 120. A pair of the hydraulic cylinders 120 moves each of a plurality of jacking pins 122 longitudinally with respect to the frame 118. The jacking pins 122 may be selectively inserted into and withdrawn from openings 116 in the exterior of the jacking leg 12 to enable the movement of the hydraulic cylinders 120 to effect longitudinally continuous movement of the jacking leg 12 up or down depending on the operation of the hydraulic cylinders 120 and jacking pins 122.

FIG. 4 shows an example embodiment of a jacking controller that may be used in some embodiments to synchronize operation of the winch (21 in FIG. 2) with operating of the jacking apparatus 12D so that the storage tank (25 in FIG. 2) is maintained a substantially constant, selected elevation. Signals from the sensor 21A on the winch (21 in FIG. 2) may be communicated to a controller 100. The controller 100 may be any type of automated process controller, including, without limitation a microprocessor with suitable power device drivers, a programmable logic controller, a field programmable gate array and an application specific integrated circuit. The controller 100 may in some embodiments form part of or be in signal communication with the DAQ (33 in FIG. 1) Signals from the jacking leg elevation sensor 124 may also be in signal communication with the controller 100. Control signals generated by the controller 100 may be used to operate the jacking apparatus, shown schematically at 16C, and the winch 21 to maintain the elevation of the storage tank (25 in FIG. 2) as the jacking leg (12 in FIG. 1) is raised or lowered.

While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims. 

1. A jackup mobile offshore drilling unit, comprising: a hull; a plurality of jacking legs movable longitudinally with respect to the hull and having features thereon to support the hull above a body of water; means for moving the jacking legs; a storage tank disposed inside at least one of the plurality of jacking legs; and means for moving the storage tank longitudinally inside the at least one of the plurality of jacking legs, wherein the means for moving the storage tank is synchronized with means for moving the at least one of the jacking legs such that the storage tank is maintained at a substantially constant elevation with respect to the hull.
 2. The jackup mobile offshore drilling unit of claim 1 wherein the means for moving comprises a winch disposed on the hull, a cable deployed from the winch and at least one sheave disposed proximate an upper end of the at least one of the plurality of jacking legs.
 3. The jackup mobile offshore drilling unit of claim 1 further comprising a reel disposed on the hull and having thereon at least one fluid transfer hose in fluid communication with an interior of the storage tank.
 4. The jackup mobile offshore drilling unit of claim 1 further comprising a storage tank disposed inside each of the plurality of jacking legs; and means for moving each storage tank longitudinally inside each of the plurality of jacking legs.
 5. (canceled)
 6. The jackup mobile offshore drilling unit of claim 1 wherein the plurality of jacking legs are each shaped as an elongated cylinder.
 7. A method for jacking a jackup mobile offshore drilling unit, comprising: operating a jacking motor to move at least one of a plurality of jacking legs longitudinally with respect to a hull of the drilling unit; operating a means for movably suspending a storage tank disposed inside the at least one of the plurality of jacking legs so as to move the storage tank to a selected elevation with respect to the hull and maintain said selected elevation as the at least one of the jacking legs moves longitudinally.
 8. (canceled)
 9. The method of claim 7 wherein the selected elevation entirely within a jacking leg opening in the hull.
 10. The method of claim 9 wherein the selected elevation is such that the storage tank is substantially entirely above a water surface. 